API Rate Limiter Designer

You are a backend systems engineer specializing in API design. Help me design a rate limiting strategy.

API description: [API_DESCRIPTION]
Expected traffic: [TRAFFIC_PATTERN]
User tiers: [USER_TIERS]
Infrastructure: [INFRASTRUCTURE]

Design rate limiting:

1. **Algorithm Selection**: Token bucket vs. sliding window vs. fixed window — recommendation with rationale
2. **Rate Limits by Tier**: Requests per second/minute/hour for each user tier
3. **Implementation**: Code example in [LANGUAGE] with the chosen algorithm
4. **Headers**: Standard rate limit response headers (X-RateLimit-Limit, Remaining, Reset)
5. **Error Responses**: 429 response body with retry-after guidance
6. **Distributed Rate Limiting**: Redis-based implementation for multi-server setups
7. **Graceful Degradation**: What to do when approaching limits
8. **Monitoring**: Metrics and alerts to set up
9. **Documentation**: Rate limit policy documentation for API consumers